WASHINGTON (AP) — Attorney General Eric Holder and a leading House Republican clashed Wednesday over the Justice Department's refusal to turn over the private emails of Thomas Perez, a top department official nominated to be labor secretary.

California Rep. Darrell Issa repeatedly pressed Holder about why the Justice Department won't release the personal emails of Perez, who heads the department's civil rights division. Issa speculated that Justice had something to hide as Republicans probe whether Perez illegally used personal email to conduct official business.

In a testy exchange, Holder told Issa that his line of questioning was "inappropriate" and "too consistent with the way in which you conduct yourself as a member of Congress."

"It's unacceptable and it's shameful," a visibly irritated Holder said at a House Judiciary Committee hearing.

Holder said he would look into the request for the emails and "we'll try to be as responsive as we can." So far, the Justice Department has only provided a few of the full emails and a list of the others identifying only sender and recipient.

"I'm sure there must have been a good reason why only the "to" and "from" parts were provided," Holder said.

"Yes, you didn't want us to see the details," Issa shot back.

The angry exchange is the latest twist in the rancorous debate between Republicans and Democrats over Perez's qualifications for the labor post. Issa and other top Republicans have accused Perez of making decisions guided by left-wing ideology rather than the pursuit of justice.

Republicans have focused their attack on a deal Perez brokered in which he persuaded the city of St. Paul, Minn., to withdraw a case from the Supreme Court. In exchange, the Justice Department agreed not to intervene in two whistle-blower cases against St. Paul that could have won up to $200 million for the federal government.

Perez has conceded that he wanted St. Paul to drop its lawsuit because there was a risk the Supreme Court would use it to strike down the government's use of statistics to prove housing discrimination cases. But he said the decisions not to intervene in the whistle-blower cases were made separately because they lacked merit.

Republicans assert that Perez overruled career attorneys at Justice who wanted to pursue the whistle-blower cases. At the hearing Wednesday, Issa played a recording of a phone message that Perez left with another Justice Department attorney asking him not to mention the Supreme Court case in a memo explaining why the government took a pass on the whistle-blower cases.

"There was a quid pro quo, there was a trade of $180 million worth of revenue to the American people in return for dropping a case that your Justice Department did not want to go before the high court," Issa said at the hearing.

Holder said the decision didn't end the case and that the private party had a right to continue litigating it. Holder says Perez sought approval before making the decision and acted in the best interests of the country. Republicans say the deal was inappropriate and claim Perez misled senior officials.

Earlier, Holder told the committee's chairman, Rep. Bob Goodlatte, R-Va., that Perez deserves praise for bringing a record number of cases alleging voting rights violations and police misconduct. He said Perez also has won record amounts of money in discrimination lawsuits.

A Senate panel is expected to endorse Perez's nomination on Thursday, despite Republican opposition.